U.S. patent application number 11/634099 was filed with the patent office on 2007-08-23 for rfid reader and method for removing a transmission carrier leakage signal.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Hee-mun Bang, Yun-seong Eo, Ick-jin Kwon, Heung-bae Lee.
Application Number | 20070194886 11/634099 |
Document ID | / |
Family ID | 38427587 |
Filed Date | 2007-08-23 |
United States Patent
Application |
20070194886 |
Kind Code |
A1 |
Bang; Hee-mun ; et
al. |
August 23, 2007 |
RFID reader and method for removing a transmission carrier leakage
signal
Abstract
A radio frequency identification (RFID) reader is provided,
having a transmitting circuit that generates a transmitted signal
to operate an RFID tag, a receiving circuit that receives a
received signal including a tag signal from the RFID tag and a
transmission carrier leakage signal leaking from the transmitting
circuit, and a leakage removing circuit that senses a phase and
amplitude of the transmission carrier leakage signal inputted to
the receiving circuit, converts the transmitted signal from the
transmitting circuit into a signal having a phase opposite to that
of the transmission carrier leakage signal and an amplitude equal
to that of the transmission carrier leakage signal, and synthesizes
the converted signal and the received signal inputted to the
receiving circuit.
Inventors: |
Bang; Hee-mun; (Seoul,
KR) ; Eo; Yun-seong; (Seoul, KR) ; Kwon;
Ick-jin; (Hwaseong-si, KR) ; Lee; Heung-bae;
(Seongnam-si, KR) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
38427587 |
Appl. No.: |
11/634099 |
Filed: |
December 6, 2006 |
Current U.S.
Class: |
340/10.1 ;
340/572.1; 455/78 |
Current CPC
Class: |
H04B 1/525 20130101;
G06K 7/0008 20130101; H04B 1/59 20130101 |
Class at
Publication: |
340/10.1 ;
455/78; 340/572.1 |
International
Class: |
H04Q 5/22 20060101
H04Q005/22 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 6, 2006 |
KR |
10-2006-0011021 |
Claims
1. A radio frequency identification (RFID) reader comprising: a
transmitting circuit which generates a transmitted signal to
operate an RFID tag; a receiving circuit which receives a received
signal including a tag signal from the RFID tag and a transmission
carrier leakage signal leaking from the transmitting circuit; and a
leakage removing circuit which senses a phase and an amplitude of
the transmission carrier leakage signal inputted to the receiving
circuit, converts the transmitted signal from the transmitting
circuit into a signal having a phase opposite to that of the
transmission carrier leakage signal and an amplitude equal to that
of the transmission carrier leakage signal, and synthesizes the
converted signal and the received signal inputted to the receiving
circuit.
2. The RFID reader of claim 1, wherein the leakage removing circuit
comprises: a gain amplifier which converts the amplitude of the
transmitted signal from the transmitting circuit; and a phase
shifter which generates an offset signal by adjusting the phase of
the transmitted signal from the gain amplifier so that the phase of
the transmitted signal becomes opposite to the phase of the
transmission carrier leakage signal.
3. The RFID reader of claim 2, further comprising a signal detector
installed on the receiving circuit which detects the transmission
carrier leakage signal inputted to the receiving circuit and the
offset signal generated through the gain amplifier and the phase
shifter.
4. The RFID reader of claim 3, wherein the leakage removing circuit
further comprises: a first switch mounted on a front end of the
signal detector on the receiving circuit which switches the input
of the received signal on/off; and a second switch arranged on a
signal line which connects the transmitting circuit and the
receiving circuit with each other to switch on/off the offset
signal to the receiving circuit.
5. The RFID reader of claim 4, wherein when the signal detector
detects the transmission carrier leakage signal, the first switch
is turned on, and the second switch is turned off.
6. The RFID reader of claim 5, wherein when the signal detector
detects the offset signal, the first switch is turned off, and the
second switch is turned on.
7. The RFID reader of claim 6, wherein when the RFID tag is
detected, both the first switch and the second switch are turned
on, and the received signal inputted to the receiving circuit and
the offset signal from the leakage removing circuit are synthesized
to remove the transmission carrier leakage signal in the receiving
circuit.
8. A radio frequency identification (RFID) reader having a
transmitting circuit generating a transmitted signal to operate an
RFID tag and a receiving circuit receiving a received signal
including a tag signal from the RFID tag and a transmission carrier
leakage signal leaking from the transmitting circuit, the RFID
reader comprising: a gain amplifier converting the amplitude of the
transmitted signal from the transmitting circuit; a phase shifter
generating an offset signal by adjusting the phase of the
transmitted signal from the gain amplifier so that the phase of the
transmitted signal becomes opposite to the phase of the
transmission carrier leakage signal; and a signal detector
installed on the receiving circuit to detect the transmission
carrier leakage signal inputted to the receiving circuit and the
offset signal generated through the gain amplifier and the phase
shifter.
9. A method for removing a transmission carrier leakage signal in a
radio frequency identification (RFID) reader, the method
comprising: measuring the amplitude and phase of a transmission
carrier leakage signal; creating an offset signal by adjusting the
transmitted signal such that the offset signal has an amplitude
equal to the transmission carrier leakage signal and a phase
opposite to the transmission carrier leakage signal; and
synthesizing the offset signal and a signal received from an RFID
tag to remove the transmission carrier leakage signal from the
received signal.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from Korean Patent
Application No. 10-2006-0011021, filed on Feb. 6, 2006, in the
Korean Intellectual Property Office, the disclosure of which is
incorporated herein by reference
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Apparatuses and methods consistent with the present
invention relate to a radio frequency identification (RFID) reader,
and more particularly, to an RFID reader which addresses problems
of signal deterioration and DC offset by effectively removing a
transmission carrier leakage signal being inputted from a
transmitting circuit to a receiving circuit, and which has a simple
circuit construction.
[0004] 2. Description of the Related Art
[0005] A ubiquitous sensor network (USN) has recently received a
lot of attention as the basic infrastructure for realizing a
ubiquitous society, which is one of the big issues in the
information and communication field. The USN is a technology that
adopts an electronic tag having a communication function, which is
attached to every object, that detects neighboring environmental
information on the basis of recognized information of the object
obtained through the electronic tag, and manages and uses the
detected information in real time through a network.
[0006] The core of the USN is an RFID system, which is composed of
a reader, an antenna, an electronic tag, a server, and a network.
Here, the reader serves to read information stored in the
electronic tag or store information in the electronic tag, and the
antenna exchanges data stored in the electronic tag by defined
frequencies and protocols.
[0007] FIG. 1 is a schematic circuit diagram of a related RFID
system composed of an RFID tag and an RFID reader 10. As
illustrated in FIG. 1, the RFID reader 10 includes a transmitting
circuit 20, a receiving circuit 25, a phase locked loop (PLL) 21,
and a processing circuit 27.
[0008] The transmitting circuit 20 generates a transmitted signal
of a specified frequency that is transferred to the RFID tag 30,
and the receiving circuit 25 receives a received signal reflected
from the RFID tag 30.
[0009] The PLL 21 is a circuit that detects a phase difference
between the transmitted signal and the received signal, and
controls the phase of a synthesizer using a voltage, which is in
proportion to the phase difference, so that the phase of the
received signal and the phase of the transmitted signal become
equal to each other.
[0010] The processing circuit 27 controls the transmitting circuit
20 to transmit the transmitted signal to the RFID tag 30, and
acquires information of the RFID tag 30 by reading the signal
received in the receiving signal 25.
[0011] The transmitting circuit 20 and the receiving circuit 25
includes an antenna 11, a filter 13, and a DC coupler 15. The
antenna 11 transmits the transmitted signal from the transmitted
circuit 20 to the RFID tag 30, and receives the received signal
reflected from the RFID tag 30 to transfer the received signal to
the receiving circuit 25. The filter 13 filters the transmitted
signal and the received signal with a desired size, and the DC
coupler 15 adjusts the DC voltages of the transmitted signal and
the received signal.
[0012] Generally, in the case of a wireless appliance, the
transmitted circuit 20 and the receiving circuit 25 operate
separately, and the signal transmitted form the transmitting
circuit 20 and the signal received in the receiving circuit 25 have
frequencies different from each other. Accordingly, the receiving
circuit 25 can be in an off state while the transmitting circuit 20
operates, and this prevents the signal transmitted from the
transmitting circuit 20 from being directly inputted to the
receiving circuit 25.
[0013] By contrast, in the case of the RFID system, since the
transmitting circuit 20 and the receiving circuit 25 use the same
frequency and the distance to the RFID tag 30 cannot be known, the
transmitting circuit 20 and the receiving circuit 25 are
simultaneously in an on state. If the transmitted signal as
illustrated in (a) of FIG. 2 is transmitted from the transmitting
circuit 20 in a state that both the transmitting circuit 20 and the
receiving circuit 25 are simultaneously in an on state, a
transmission carrier leakage signal as illustrated in(d) of FIG. 2
is directly inputted to the receiving circuit 25 through the
antenna.
[0014] If the transmission carrier leakage signal is inputted to
the receiving circuit 25 as described above, it acts as a noise,
and a signal obtained by addition of the transmission carrier
leakage signal to the received signal from the RFID tag 30 as
illustrated in (b) of FIG. 2 is received in the receiving circuit
25, as illustrated in (e) of FIG. 2. Accordingly, although the
received signal that can be obtained by filtering when no
transmission carrier leakage signal exists is as shown in (c) of
FIG. 2, the received signal that can be obtained by filtering when
the transmission carrier leakage signal exist is as shown in (f) of
FIG. 2, so that it is almost impossible to obtain the received
signal from the RFID tag 30. As a result, problems of signal
deterioration and DC offset may occur.
[0015] In addition, each component of the receiving circuit 25,
e.g., a low noise amplifier (LNA) or a mixer, is designed to
receive an input of a small-sized received signal from the RFID tag
30, and its linearity is low. Accordingly, if a large transmission
carrier leakage signal is inputted from the transmitting circuit
20, the LNA of the receiving circuit 25 is saturated, resulting in
an inoperable state.
[0016] In order to solve this problem, Mitsubishi Electric Corp. of
Japan has developed a canceller circuit 55 that removes the
transmission carrier leakage signal, as illustrated in FIGS. 3A and
3B.
[0017] As illustrated in FIGS. 3A and 3B, the canceller circuit 55
is positioned on a line connecting the transmitting circuit and the
receiving circuit with each other, and includes an amplitude phase
adjustment circuit 75, an amplitude phase comparison circuit 73, a
pair of integrators 78 and 79, an adder 77, and a pair of couplers
70 and 71.
[0018] The amplitude phase comparison circuit 73 detects the
amplitude and the phase of the received signal inputted to the
receiving circuit, and transfers an amplitude error and a phase
error, which have passed through the integrators 78 and 79,
respectively, to the amplitude phase adjustment circuit 75.
[0019] The amplitude phase adjustment circuit 75 receives a
non-modulated signal generated from the transmitting circuit and
the amplitude error and the phase error from the amplitude phase
comparison circuit 73, and adjusts the amplitude and the phase of
the received signals. In this case, the amplitude phase adjustment
circuit 75 generates an adjusted signal by adjusting an unmodulated
signal generated from the transmitting circuit so that the adjusted
signal has an amplitude equal to that of the unmodulated signal and
a phase opposite to that of the unmodulated signal.
[0020] The adder 77 adds the adjusted signal adjusted by the
amplitude phase adjustment circuit 75 to the received signal to
remove the diffracted transmission carrier leakage signal from the
transmitting circuit.
[0021] However, since the related canceller circuit 55 is composed
of a plurality of circuits, integrators 78 and 79, and others, and
requires couplers 70 and 71 to receive the signals from the
transmitting circuit and the receiving circuit, the circuit
construction of the RFID reader becomes complicated. In addition,
the errors may become greater due to the difference between the
bidirectional output characteristics of the couplers 70 and 71, and
the feedback circuit using the integrators 78 and 79 may become
unstable due to its characteristics.
SUMMARY OF THE INVENTION
[0022] Exemplary embodiments of the present invention overcome the
above disadvantages and other disadvantages not described above.
Also, the present invention is not required to overcome the
disadvantages described above, and an exemplary embodiment of the
present invention may not overcome any of the problems described
above.
[0023] The present invention has been developed in order to address
the above drawbacks and other problems associated with the related
arrangement. An aspect of the present invention is to provide an
RFID reader which can solve problems of signal deterioration and DC
offset by effectively removing a transmission carrier leakage
signal being inputted from a transmitting circuit to a receiving
circuit, and which has a simple circuit construction.
[0024] According to an aspect of the present invention, there is
provided a radio frequency identification (RFID) reader, including
a transmitting circuit that generates a transmitted signal to
operate an RFID tag, a receiving circuit that receives a received
signal including a tag signal from the RFID tag and a transmission
carrier leakage signal leaking from the transmitting circuit, and a
leakage removing circuit that senses a phase and an amplitude of
the transmission carrier leakage signal inputted to the receiving
circuit, converts the transmitted signal from the transmitting
circuit into a signal having a phase opposite to that of the
transmission carrier leakage signal and an amplitude equal to that
of the transmission carrier leakage signal, and synthesizes the
converted signal and the received signal inputted to the receiving
circuit.
[0025] The leakage removing circuit may include a gain amplifier
that converts the amplitude of the transmitted signal from the
transmitting circuit, and a phase shifter that generates an offset
signal by adjusting the phase of the transmitted signal from the
gain amplifier so that the phase of the transmitted signal becomes
opposite to the phase of the transmission carrier leakage
signal.
[0026] The RFID reader may further include a signal detector
installed on the receiving circuit that detects the transmission
carrier leakage signal inputted to the receiving circuit and the
offset signal generated through the gain amplifier and the phase
shifter.
[0027] The leakage removing circuit may further include a first
switch mounted on a front end of the signal detector on the
receiving circuit that switches the input of the received signal
on/off, and a second switch arranged on a signal line that connects
the transmitting circuit and the receiving circuit with each other
to switch on/off the offset signal to the receiving circuit.
[0028] When the signal detector detects the transmission carrier
leakage signal, the first switch may be turned on, and the second
switch may be turned off.
[0029] When the signal detector detects the offset signal, the
first switch may be turned off, and the second switch may be turned
on.
[0030] When the RFID tag is detected, both the first switch and the
second switch are turned on, and the received signal inputted to
the receiving circuit and the offset signal from the leakage
removing circuit are synthesized to remove the transmission carrier
leakage signal in the receiving circuit.
[0031] According to another aspect of the present invention, there
is provided a radio frequency identification (RFID) reader having a
transmitting circuit that generates a transmitted signal to operate
an RFID tag and a receiving circuit that receives a received signal
including a tag signal from the RFID tag and a transmission carrier
leakage signal leaking from the transmitting circuit, which
includes a gain amplifier that converts the amplitude of the
transmitted signal from the transmitting circuit, a phase shifter
that generates an offset signal by adjusting the phase of the
transmitted signal from the gain amplifier so that the phase of the
transmitted signal becomes opposite to the phase of the
transmission carrier leakage signal, and a signal detector
installed on the receiving circuit that detects the transmission
carrier leakage signal inputted to the receiving circuit and the
offset signal generated through the gain amplifier and the phase
shifter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The above and other aspects of the present invention will be
more apparent by describing certain exemplary embodiments of the
present invention with reference to the accompanying drawings, in
which:
[0033] FIG. 1 is a schematic circuit diagram of a related RFID
system composed of an RFID tag and an RFID reader 10;
[0034] FIG. 2 are graphs illustrating a transmission carrier
leakage signal, an RFID tag signal, and a received signal generated
in the RFID system of FIG. 1;
[0035] FIGS. 3A and 3B are circuit diagrams of a canceller circuit
in a related RFID system and an RFID reader adopting the
canceller;
[0036] FIG. 4 is a circuit diagram of an RFID reader having a
leakage removing circuit according to an exemplary embodiment of
the present invention; and
[0037] FIG. 5 is a detailed circuit diagram of a circuit part
through which the leakage removing circuit of FIG. 4 and a
receiving circuit are connected to each other.
[0038] FIG. 6 is a flowchart diagram showing the process for
removing a transmission carrier leakage signal in an RFID system
according to an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS OF THE
INVENTION
[0039] Certain exemplary embodiments of the present invention will
be described in greater detail with reference to the accompanying
drawings.
[0040] FIG. 4 is a circuit diagram of an RFID reader having a
leakage removing circuit 150 according to an exemplary embodiment
of the present invention.
[0041] As illustrated in FIG. 4, the RFID reader according to the
present invention includes a transmitting circuit 121, a receiving
circuit 111, a leakage removing circuit 150, and directional
coupler 112.
[0042] The transmitting circuit 121 includes a pair of input
buffers 128, a pair of low pass filters (LPFs) 126, a variable
amplifier 124, and a balun 123.
[0043] The respective input buffers 128 amplify quadrature signals
(i.e., I-signal and Q-signal) from a processing circuit (not
illustrated) that controls transmission, and generate a transmitted
signal at a specified level. The respective LPFs 126 filter the
quadrature signals (i.e., I-signal and Q-signal) from the
respective buffers 128, and generate the quadrature signals having
a desired amplitude.
[0044] The variable amplifier 124 combines the quadrature signals
(I-signal and Q-signal) from the respective buffers 128 with
differential signals from a synthesizer 119, and outputs
differential signals of the I-signal and the Q-signal. The balun
123 converts the differential signals of the I-signal and the
Q-signal from the variable amplifier 124 into a single transmitted
signal. The transmitted signal from the balun 123 passes through
the directional coupler 112, and then is transmitted to an RFID tag
through a transmission antenna 120.
[0045] On the other hand, the receiving circuit 111 includes a
balun 113, a low noise amplifier (LNA) 114, a pair of down mixer
115, a pair of filters 116, a pair of variable gain amplifiers 117,
and a pair of buffers 118.
[0046] The balun 113 converts the received signal, which has been
received through a reception antenna 110 and has passed through the
directional coupler 112, into a differential signal. The LNA 114
amplifies the received signal received through the antenna.
[0047] The pair of down mixers 115 receive the received signal
having been amplified through the LNA 114, and down-convert the
received signal into a baseband signal using the differential
signal from the synthesizer 119 to generate quadrature signals
(i.e., I-signal and Q-signal).
[0048] The respective filters 116 remove noise from the quadrature
signals (I-signal and Q-signal) having the baseband frequency by
filtering the quadrature signals by a desired amplitude. The
respective variable gain amplifiers 117 amplify the quadrature
signals (I-signal and Q-signal) from the respective filters
116.
[0049] The synthesizer 119, which provides the differential signals
to the variable amplifier 124 of the transmitting circuit 121 and
the down mixer 115 of the receiving circuit 111, generates the
differential signals having diverse frequencies for use in the
RFID, and in this case, the frequency of the differential signal
generated from the synthesizer 119 is equal to that of a center
frequency of the transmitted signal. The synthesizer 119 is
connected to a reference oscillator 129, and receives a signal from
the reference oscillator 129.
[0050] The directional coupler 112 is provided between the
transmission antenna 120 and the reception antenna 110 on one hand,
and the respective baluns 113 and 123 on the other. The directional
coupler 112 is provided with a pair of direct paths through which
the transmitted signal from the transmitting circuit 121 and the
received signal from the receiving circuit 111 are directly
transmitted and received, respectively, and a pair of cross paths
through which the received signal and the transmitted signal cross
each other. Here, since the cross paths have a negative (-) loss
that is lower than that of the direct paths, they can attenuate the
received signal and the transmitted signal, and thus reduce the
influence of the signals inputted from the transmitting circuit 121
to the receiving circuit 111 through the directional coupler
112.
[0051] Between the transmitting circuit 121 and the receiving
circuit 111 as described above, the leakage removing circuit 150 to
remove the transmission carrier leakage signal from the
transmitting circuit 121 is installed.
[0052] The leakage removing circuit 150 includes a signal detector
145, a gain amplifier 151, and a phase shifter 155. The gain
amplifier 151 and the phase shifter 155 are arranged on a pair of
signal lines that connect the transmitting circuit 121 and the
receiving circuit 111 with each other, and this pair of signal
lines are connected between connection points of the balun 123 of
the transmitting circuit 121 and the variable amplifier 124 and
connection points of the balun 113 of the receiving circuit 111 and
the LNA 114.
[0053] FIG. 5 is a detailed circuit diagram of a circuit part
through which the leakage removing circuit of FIG. 4 and a
receiving circuit are connected to each other.
[0054] Referring to FIG. 5, a pair of first switches 156 are
connected between the signal detector 145 and the balun 113, and
are simultaneously turned on/off to intercept the signal and the
transmission carrier leakage signal between the reception antenna
110 and the receiving circuit 111. Also, a pair of second switches
157 are connected between the phase shifter 153 and the receiving
circuit 111, on the respective signal lines, and intercept the
input of the transmitted signal generated from the transmitting
circuit 121 to the receiving circuit 111. On the other hand, a
buffer 159 is connected between the second switch 157 and the
receiving circuit 111.
[0055] The signal detector 145 detects the amplitude and the phase
of the transmission carrier leakage signal inputted from the
transmitting circuit 121 to the receiving circuit 111 for an
adjustment time when a power is supplied to the RFID reader and the
transmitting circuit 121 is in an on state. At this time, by
intercepting the power supplied to the receiving circuit 111, the
components, including the LNA, are prevented from being saturated
due to the transmission carrier leakage signal.
[0056] When the signal detector 145 detects the transmission
carrier leakage signal as described above, the first switch 156 is
turned on to allow the transmission carrier leakage signal to be
inputted, while the second switch 157 is turned off to intercept
the input of the transmitted signal from the transmitting circuit
121 to the receiving circuit 111.
[0057] The gain amplifier 151 receives the transmitted signal
generated from the transmitting circuit 121, and adjusts the gain
of the transmitted signal. That is, the gain amplifier 151 adjusts
the gain of the transmitted signal in accordance with the amplitude
of the transmission carrier leakage signal detected through the
signal detector 145, so that the amplitude of the transmission
carrier leakage signal and the amplitude of the transmitted signal
become equal to each other.
[0058] The phase shifter 155 adjusts the phase of the transmitted
signal, of which the amplitude has been adjusted by the gain
amplifier, so that the phase of the transmitted signal becomes
equal to the phase of the transmission carrier leakage signal, by
shifting the phase of the transmitted signal, and inverts the phase
of the transmitted signal. Accordingly, the transmitted signal from
the transmitting circuit 121 has the phase opposite to the phase of
the transmission carrier leakage signal inputted to the receiving
circuit 111 to act as an offset signal.
[0059] The offset signal, which has the amplitude equal to that of
the transmission carrier leakage signal and the phase opposite to
that of the transmission carrier leakage signal, through the gain
amplifier 151 and the phase shifter 155, is provided to the
receiving circuit 111, and then is synthesized with the received
signal inputted to the receiving circuit 111 to remove the
transmission carrier leakage signal included in the received
signal. In this case, the first and second switches 156 and 157 are
all turned on, so that the received signal is inputted to the
receiving circuit 111 and the transmitted signal from the
transmitting circuit 121 is converted into the offset signal
through the leakage removing circuit 150.
[0060] The process of removing the transmission carrier leakage
signal through the RFID system as seen in FIG. 6 will now be
explained.
[0061] If the power is supplied to the RFID reader, a control unit
(not illustrated) turns on the first switch 156 and turns off the
second switch 157 to measure the amplitude and the phase of the
transmission carrier leakage signal using the leakage removing
circuit 150 (S601). Accordingly, the transmission carrier leakage
signal from the transmitting circuit 121 is inputted to the signal
detector 145 after passing through the first switch 156. The signal
detector 145 detects the transmission carrier leakage signal and
stores the detected signal in a memory (not illustrated) and so
on.
[0062] Then, the control unit turns off the first switch 156 and
turns on the second switch 157. Accordingly, the transmitted signal
from the transmitting circuit 121 is adjusted through the gain
amplifier 151 and the phase shifter 155 of the leakage removing
circuit 150, so that an offset signal having an opposite phase is
generated. The signal detector 145 detects the offset signal
generated through the gain amplifier 151 and the phase shifter 155.
The control unit adjusts the gain of the gain amplifier 151 and the
phase of the phase shifter 155 until the offset signal has the
amplitude equal to that of the transmission carrier leakage signal
and the phase opposite to that of the transmission carrier leakage
signal (S602).
[0063] As described above, the power is not supplied to the
receiving circuit 111 until the amplitude and the phase of the
transmission carrier leakage signal are measured, and the offset
signal from the transmitting circuit 121 has the phase opposite to
that of the transmission carrier leakage signal and the amplitude
equal to that of the transmission carrier leakage signal.
[0064] If the transmitted signal is converted into the offset
signal having the amplitude equal to that of the transmission
carrier leakage signal and the phase opposite to that of the
transmission carrier leakage signal through the leakage removing
circuit 150, the control unit turns on both the first switch 156
and the second switch 157. In this case, the transmitted signal
from the transmitting circuit 121 is transmitted to the RFID tag,
and the signal reflected from the RFID tag and the transmission
carrier leakage signal from the transmitting circuit 121 are
synthesized, so that the synthesized signal is inputted to the
receiving circuit 111 as the received signal (S603).
[0065] The input received signal is synthesized with the offset
signal generated through the leakage removing circuit 150, and the
transmission carrier leakage signal is removed from the received
signal by the offset signal. Accordingly, the signal from the RFID
tag, as illustrated in FIG. 2(b), is inputted to the LNA of the
receiving circuit 111.
[0066] The RFID reader includes the leakage removing circuit 150
that has a simple construction composed of the signal detector 145,
the gain amplifier 151, and the phase shifter 155, and removes the
transmission carrier leakage signal.
[0067] As described above, according to an exemplary embodiment of
the present invention, the transmission carrier leakage signal is
effectively attenuated, and thus the problems of signal
deterioration and DC offset can be solved. Also, as the desired
linearity terms of components of the receiving circuit, such as an
LNA and a down mixer, become easy, the saturation of the LNA and
the down mixer can be prevented. Also, since the magnitude of the
transmitted signal is increased, the dynamic range of the RFID
reader is increased even without increasing the sensitivity of the
RFID tag, and thus the communication distance between the RFID
reader and the RFID tag can be increased. In addition, since the
circuit construction of the RFID reader can be simplified, its
manufacturing process becomes easy with its manufacturing cost
reduced.
[0068] The foregoing embodiment is merely exemplary and is not to
be construed as limiting the present invention. The present
teaching can be readily applied to other types of apparatuses.
Also, the description of the exemplary embodiments of the present
invention is intended to be illustrative, and not to limit the
scope of the claims, and many alternatives, modifications, and
variations will be apparent to those skilled in the art.
* * * * *